A relay valve according to the prior art accelerates the admission and release of air, e.g. to and from the brake cylinders. It acts as a valve which boosts the volume of air inasmuch as the relay valve controls relatively large volumes of compressed air, e.g. for the brake cylinders of an air braking system of a vehicle, with relatively small volumes of air.
In conventional arrangements, the relay valve has a housing, which has a pressure medium inlet that can be connected to a pressure medium source, at least one pressure medium outlet that can be connected to a consuming unit, at least one control inlet, and at least one vent leading to atmosphere. The relay valve furthermore has a relay valve piston, which is arranged in the housing in such a way that the relay valve piston can be moved along a relay valve piston axis and divides a control chamber and a working chamber from each other in the housing.
On one side, the relay valve piston can thus be subjected via the control chamber to control pressure and, on the other side, it can be subjected via the pressure medium outlet to a working pressure provided by a consuming unit.
An inlet valve is arranged between the working chamber and an air admission chamber that can be connected via the pressure medium inlet to the pressure medium source, and an outlet valve is arranged between the working chamber and a venting chamber leading to atmosphere.
When the control chamber is supplied with a pressure medium, the relay valve piston moves into the working chamber in accordance with the control pressure of the pressure medium. In the course of this movement, the relay valve piston first of all closes the outlet valve and then opens the inlet valve counter to the force of a spring. By virtue of the connection established between the air admission chamber and the working chamber, a pressure builds up in the working chamber, counteracting the control pressure on the relay valve piston.
When there is substantially an equilibrium between the forces caused by the pressures on the relay valve piston, the relay valve piston is pushed back counter to its original movement. During this process, the inlet valve is closed, without however opening the outlet valve, with the result that the pressure in the working chamber and in the consuming units connected via the pressure medium outlet is maintained.
If the control chamber is partially or completely vented, the relay valve piston moves further, counter to its original direction of movement, and the outlet valve opens. The pressure in the working chamber then falls to a value at which there is once again an equilibrium of forces on the relay valve piston and the outlet valve is closed again. If the control chamber is completely vented, the working chamber is also completely vented, leading to venting of the downstream consuming units. A relay valve operating in this way is known from EP 1 844 999 A1, for example.
Conventional relay valves of this kind are generally integrated into a valve device together with further components, in particular a valve device having a pilot control unit and at least one relay valve. Such valve devices are used in pneumatic systems, such as braking systems or air suspension systems for commercial vehicles.
However, supplying the control chamber of the relay valve with a pressure medium can lead to oscillations of the relay valve piston since the relay valve piston, together with the control chamber volume, which acts as an air spring, represents an oscillatory system. Such oscillations arise preferentially in the case of cyclical excitation of the relay valve and can lead to destruction of the relay valve.
A possible embodiment of the relay valve to avoid oscillations of the relay valve piston is shown in DE 102 38 182 A1. A sealed partition wall arranged in the working chamber has a device for pressure compensation. Here, the partition wall has the function of a baffle and shields the relay valve piston from the dynamic gas flow forces. However, unwanted pronounced pressure peaks can arise in this arrangement, depending on the size of the consuming units connected.